1. Field of the Invention
The present invention relates to metal-oxide based memory devices, methods for manufacturing such devices, and methods for operating such devices.
2. Description of Related Art
Various metal-oxide materials have been proposed for use in high density one-time programmable (OTP) memory having diode access devices. Metal-oxide based OTP memory is programmed by applying a voltage across the metal-oxide material to cause a permanent change in the resistance of the material. A representative high density metal-oxide OTP memory having diode access devices is shown in U.S. Pat. No. 7,053,406.
Electrically erasable and reprogrammable nonvolatile memory offers more flexibility than OTP memory since the information stored can be written and erased numerous times. Some metal-oxides can be caused to reversibly change resistance between two or more stable resistance ranges by application of electrical pulses at levels suitable for implementation in integrated circuits, thus providing a basis for use in nonvolatile resistive random access memory RRAM.
Transistor access devices have been proposed as drivers for metal-oxide based electrically erasable and reprogrammable nonvolatile memory. See, for example, U.S. patent application Ser. No. 11/955,137. However, transistors have a large cross-sectional area than diodes and thus suffer from a lower memory density than OTP memory devices using diode access devices.
It is therefore desirable to provide an electrically erasable and reprogrammable metal-oxide based memory cell structure having diode access devices for use in high-density memory devices. It is also desirable to provide methods for manufacturing which address the tight process requirements needed for large-scale high density devices.